1. Field of Invention
The present invention provides an ink composition for ink jet recording, which, even on various recording media, especially printing paper for running-on, can yield images having excellent gloss and color reproduction and, at the same time, can realize excellent ejection stability and recovery from clogging, and a method for ink jet recording using the ink composition.
2. Background Art
Ink jet recording is a printing method wherein droplets of an ink are ejected and deposited on recording media, such as paper, to perform printing. An innovative advance of a recent ink jet recording technique has made it possible to realize the production of images having quality comparable to images produced by silver salt photography or images yielded by high-definition printing realized only by offset printing. This trend has led to the development of inks for ink jet recording that can realize images having a high level of glossy impression comparable to the gloss of images produced by silver salt photography, using the so-called specialty papers which are recording media having a high level of gloss comparable to photographic paper, art paper and the like used in the field of silver salt photography and offset printing. Further, inks for ink jet recording which can realize image quality comparable to the image quality of images produced by silver salt photography even on plain paper, have also been developed.
Inks, which have been generally used for ink jet recording, are water-based inks that comprise water as a main component and a colorant and various additives. Regarding the colorant, the development of pigment-based inks utilizing the properties of the pigment has recently been forwarded because pigments are superior to dyes in weatherfastness properties such as lightfastness, gasfastness, waterfastness, and moisturefastness. For example, Japanese Patent Laid-Open No. 194500/2005 discloses a pigment-based ink composition having feathering- or bleeding-free properties and excellent gloss on specialty papers that have been realized by using a polysiloxane compound as a surfactant and adding an alkanediol such as 1,2-hexanediol as a solubilizer additive to the ink. Further, Japanese Patent Laid-Open Nos. 72905/2001 and 12583/2003 disclose an ink containing 1,2-hexanediol, which is a water soluble alkanediol, and 1,2-octanediol, which is a slightly water soluble alkanediol, as additives. The claimed advantage of this ink is feathering- or bleeding-free properties on plain papers. Further, Japanese Patent Laid-Open No. 263970/2005 discloses an ink composition comprising an acetylene glycol compound and a polysiloxane compound as surfactants and further 1,2-octanediol. The claimed advantage of this ink composition is to realize high print density on plain paper.
The widespread use of techniques for forming images from digital data in recent years has led to an increased need for digital color proofs (DTPs) particularly in the field of printing, and an ink jet recording method has also become applied to DTPs. The color reproduction and stability reproduction of printed matters are required of DTPs. Accordingly, when proofs are prepared by the ink jet recording method, specialty paper for ink jet recording has been generally used. In applications for color proof, however, ink jet recording on printing paper for running-on rather than specialty papers has been highly desired. Further, it is considered that proof cost can be significantly reduced if printed matter output directly on printing paper for running-on can be used as a final proof sample without use of any specialty paper. The printing paper for running-on is a coated paper having on its surface a coating layer for receiving an oil-based ink. In the printing paper for running-on, however, the capability of the coating layer to absorb ink is disadvantageously poor. Therefore, when water-based pigment inks, which have been generally used in ink jet recording, are used, the penetrability of the inks into recording media is so low that feathering or bleeding or uneven coagulation sometimes occurs in images.
When a high-penetration ink comprising the above polysiloxane surfactant and 1,2-hexanediol as a solubilizer for the polysiloxane surfactant is used from the viewpoint of solving the above problem, the feathering or bleeding problem can be reduced, but on the other hand, a problem of a difference in color reproduction between proofs and final printed matters and a problem of stable color reproduction sometimes take place.